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After driving my SS for one full season since I bought it, I was quite impressed with the overall balance of the car in steady-state maneuvers. The OEM springs, while too tall for many people's tastes, are in fact a nice comfortable stiffness and provide pretty good handling. The stock sway bars (on an SS anyway) and the stock tires are also a pretty good combination. The whole thing is pretty well ruined however by the unbelievably bad DeCarbon shocks. My Montana mini-van has better feeling shocks.
I chose to upgrade with Koni Single Adjustable Shocks for a number of reasons but for the most part I wanted the ability to adjust for spring changes I might make in the future. I discuss this more below.
Since the rear shocks are so simple to change I started with them. Total swap time was about 1 hour for both rear shocks.
Dealing with the carpet in a convertible is different that in a coupe. www.ls1howto.com shows a coupe shock swap. Where the cargo floor of a coupe is level before dropping down behind the rear seat, the convertibles have a substantial reinforcement piece welded across behind the seat. The floor rises over this hump before going down behind the seat. Instead of the top of the shock being accessible from above as in a coupe the shock top is buried under the extra metal and requires reaching in through a window that was left for access.
The rear shocks are still quite easy to swap out. Start with lowering the rear seat. Remove the plastic cap covering the front seat belt. Undo the large Torx bolt that is also the rear seat striker. With that removed the whole side panel will lift out, it is only held along its front edge (near the door) and tucks under the trim piece covering the door sill. There is no need to remove anything else.
You can see in the photo where the shock mount is. The carpet is pre-perforated in the right place already. I just used a knife to make an actual slit in the carpet where the perforations are. Stuffed into the hole is a foam blob (also in the photo) that you need to pull out. In this photo, the shock has already been swapped. I used vice grips on the flats at the tip of the shock and used a box end wrench on the nut. This part of the car should be rust free so removal should not normally be a problem.
Here is a good view of the whole shock and the lower mounting bolt. With the nut removed inside the car, the whole shock just falls out once the lower nut is removed.
Changing the front shocks is much more involved. www.ls1howto.com has a full article on this swap but with Bilstein shocks. The Konis are slightly different in that the adjustment window must be installed facing outward so that the adjustments can be made once the shocks are back on the car.
View of shock bottom and bolts securing it to lower arm. Also visible is the sway bar link that must be released.
Since the spring is safely contained on the shock, it is safe to undo almost any fastener. Nothing will jump out and kill you like it could on my previous car a Buick Turbo-T. You can do much of the following in any order but I will list it in the order I did it.
Lift the hood, remove shock mount fasteners. On the passenger side, remove the 2 13mm head bolts and 2 15 mm nuts securing the shock/upper arm mount to the car body. The inner bolt is somewhat under an AC line and care must be taken not to damage it.
On the driver side there are 2 TorxT-50 head bolts instead and 2 15 mm nuts. The problem is that the outboard Torx bolt is crammed under the master cylinder. The service manual suggests removing the master cylinder nuts and carefully flexing it out of the way. I found that difficult so I did it a bit differently. There are 2 hard lines from the master cylinder over to the ABS unit. The ABS unit output lines are braided flexible lines. When you release the ABS from its mount you can slide it and the master cylinder forward together.
Remove the 2 nuts on the sides of the ABS, reach under and pry up with your fingers and the unit will pop up off the rubber peg it sits on. Hold the master cylinder and the ABS together and they both slide forward as shown.
Here you can see the clearance available. Both bolt holes are fully accessible letting you remove and properly torque the fasteners when they are put back in place later.
To release the ball joint, start by removing the cotter pin and back the castellated down the stud section of the joint. Do not remove it fully yet. To release it, I used a pickle fork show below. The problem with pickle forks is that they can damage the rubber boot in the ball joint. I greased the fork prongs to let it slide in without ripping the rubber and it seemed to help. Drop the car's weight onto the lower control arm with a jack or jack stand under the arm. This compresses the spring and raises the upper arm to let the fork get in at the ball joint without hitting the arm itself. With the fork seated, a light hammer blow popped it free. Then I released the nut and popped the joint apart.
Once the joint was apart I tied the rope as shown to keep the brake line from being pulled taught. The rope lets you move the spindle all over the place for access but kept the brake line at a constant length.
Remove the sway bar link and then undo the two bolts holding the shock to the lower arm. The wrench in the photo is hanging on of the bolts. On my car I had to push the lower arm down pretty hard to get the strut to come down out of the tower and come free.
This is the potentially dangerous part. The spring stores a lot of potential energy and must be handled properly. The factory manual shows a large set of tooling meant to be used in a press. Most people are going to be using spring compressors. I have heard of people releasing the spring and letting it rocket across the room but I was not to keen on doing that.
The upper control arm is just sitting there. It just gets sandwiched between the tower in the car and the shock when it is in the car. It just lifts off.
The factory did not vent the top of the shock mount very well so moisture doesn't boil off. This is the passenger side shock and the nut was really rusty. I used a wire brush mounted in a die grinder to clean it off. After putting on the spring compressors shown below and squashing down the spring, I tried to turn the nut while holding the shaft by the flat section. It refused to budge so I used an impact wrench on it. That backed the nut half way off before it got stuck again. I wound up using a die grinder a carbide burr to cut through the nut. The driver side nut came right off with the impact wrench.
Side by side view of of the new and old shocks. You can see the mangled threads where I wound up cutting into the threads while grinding off the nut.
The Koni shocks allows you to choose one of two spring perch heights. The spring perch just slides up and out of the way while you change the ring clip position. I just used my fingers to peel up the end of the ring and move it down to the lower perch position. The slots are approximately 3/8" apart. Since the shock mounts only half way out along the lower control arm, the lever action on the control arm winds up being approximately 3/4" in ride height lower than stock.
This is the shock and spring reassembled. The top nut is supposed to be torqued to 33 ft.lb but I could not get the wrench in on the top nut while holding the flats on the tip of the shaft. Instead I inserted slip joint pliers into the coil spring and around the adjustment window portion of the shock which you can see between the first and second coil. Then I was able to tighten the nut probably to 25 ft.lbs or so before the shock started to slip in the plier jaws. It was difficult keeping the adjustment window pointing the right way while tightening things but you need to have access to it when the car is back together.
On stock springs and sitting on the lower perch and with the car sitting on the ground normally, the adjustment window is visible just over the top of the tire.
While I had the nuts off I added a Spohn strut tower brace. If you are adding one do NOT buy a Chrome Molybdenum version, you pay more for a lighter bar. Chrome Molybdenum is a higher grade steel alloy known for its strength, but STBs never break. The whole point is to add stiffness to the car, not strength. Since all carbon steels have the same stiffness, and density, the Chrome Molybdenum version, being lighter is simply less stiff. Save your money.
There are a lot of misconceptions about these bars. Some people claim that since these cars do not have Macpherson struts that these bars cannot do anything. All the lateral loads (including front to back loading, especially during braking) in the spindle are reacted by the two ball joints. The ball joints are the only thing holding the wheel in place. The wheel axis is very low down close to the lower control arm. The lever arm ratio makes the upper arm loads 1/3 to 1/4 of those at the bottom arm. The loads at the upper arm, small as they are, only go into the tower. So, by design, the upper arm and tower do not need to be as stiff as the lower arm and the sub-frame. You can tell this is true by looking at the two arms, the upper one is quite light and slim, the lower one is much beefier.
During a hard turn, you could easily see a 1000-1500 lb lateral load on the suspension, primarily on the side at the outside of the turn. By design, the towers can be less stiff than the frame below because the loads are much smaller. The smaller upper arm loads will deflect the tower by a finite amount. The suspension on the other side deflects less because there is less load on it since the outer tire carries a bigger load. This is the key point, rather than let one tower move more than the other, the STB is a convenient and simple way to tie the 2 sides together and add some net stiffness to the car by bracing the tower seeing the bigger load to the tower that is less loaded. The car's towers may be stiff enough not to need an STB, but this has nothing to do with the fact that it has no struts versus having control arms.
The STB is only going to keep the tower spacing fixed it cannot help with a tower trying to rise more than the other or with one trying to move rearward compared to the other one. One main argument against them is that the car's handling is not improved. On a skid pad or a smooth off ramp, an STB probably does very little. However the car's behaviour over bumps will be tighter, especially on a convertible. This is the main reason I have added the bar. If you are looking to improve your handling, you are probably better off doing something else. If you want to tighten things up then this is where the STB should help. Disagree? Tell me why!
What most people do not realize, is how much the overall feel of a car depends on the design of the shock absorbers. A shock that is mismatched to the springs on the car can ruin the performance of even the best designed suspension (like the DeCarbons). What separates a high and low quality shock is the design of the valving. Like many things you get what you pay for.
When you hit a rock or bump you want the suspension to retract out of the way quickly. The shock absorbers are viscous dampers so they resist movement in both directions. Ideally you have very little damping to collapse the shock in order to minimize the loads transmitted into the car body. You then want to have a lot more damping as the suspension extends again to control the car movement.
For those of us who like to change spring rates, the appropriate amount of damping varies quite a bit. A stiffer spring moves through a smaller range of motion when you hit a bump. The shock absorbs energy over its travel distance so a stiffer spring needs a stiffer shock to absorb the same energy over the shorter stroke in order to feel right and reap the benefits of the stiffer spring. Since the shock is quite soft in the jounce stroke, most of the energy is absorbed during the rebound stroke. Therefore not being able to adjust the jounce damping is not a problem for most cars. The ability to dial in your car depends a lot more on the rebound damping which is what the Koni SAs let you adjust. With the stock springs I find the jounce damping to be on the side of comfortable. I also find that I drive with the rear at full soft and the front one sweep stiffer than full soft for the best compromise of handling and comfort.